Cat's Eye
“Cat’s eye” is a phenomenon name before it is a stone name, and that ambiguity is worth clearing up before anything else: chatoyancy — the bright, moving line of light that gives the effect its name — can appear in several different gem species, including tourmaline, quartz, and apatite. But when the trade uses the bare term “cat’s eye” with no qualifier, it means one specific gem: chrysoberyl cat’s eye, also called cymophane. Every other chatoyant gem is named explicitly with its species attached, precisely so buyers aren’t misled about what they’re getting.
Species and variety. Cat’s eye (cymophane) is a variety of chrysoberyl, BeAl2O4, the same species behind alexandrite — though the two chrysoberyl varieties are prized for different optical effects and a stone rarely shows both strongly. Chrysoberyl cat’s eye owes its chatoyancy to dense, parallel, needle-like inclusions inside the crystal; cut as a smooth-domed cabochon (never faceted, which would destroy the effect), those inclusions reflect incoming light into a single sharp band that appears to open and close as the stone is turned.
Appearance and color range. Chrysoberyl cat’s eye typically shows a honey-yellow to yellowish-green or brownish body color, with a “milk and honey” effect prized in the finest stones — one half of the dome appearing milky white, the other honey-gold, as the stone is tilted under a single light source. The sharpness and centering of the eye line matter as much to value as the body color.
Hardness and everyday care. At 8.5 on the Mohs scale, chrysoberyl cat’s eye is highly durable, tougher than most colored gems worn in jewelry, and well suited to rings. Its cabochon cut, being domed rather than faceted, is also somewhat more resistant to chipping at the edges than a faceted stone of similar hardness.
Where it is found. Sri Lanka is the classic and most prized source of chrysoberyl cat’s eye, with additional material from Brazil, India, and Russia.
Birthstone role. Cat’s eye appears in the historical (pre-20th-century) monthly list for June, alongside turquoise and agate — a three-stone month typical of the looser older tradition. None of the three modern systems (US 1912, UK 2013, US current) retain it; today’s June belongs to pearl, moonstone, and, in the US current system, alexandrite instead.
Gemmological properties
| Mohs hardness | 8.5 |
|---|---|
| Crystal system | Orthorhombic |
| Chemical formula | BeAl2O4 |
| Refractive index | 1.746–1.755 |
| Color family | Yellow, Green, Brown |
| Variety of | chrysoberyl |
| Also known as | cymophane, chrysoberyl cat's eye |
| Origins | Sri Lanka, Brazil, India, Russia |
| Organic material | No |
The unqualified term cat's eye, used in the trade, traditionally means chrysoberyl cat's eye (cymophane); other species that show chatoyancy are named explicitly instead, e.g. tourmaline cat's eye.
Where Cat's Eye appears as a birthstone
By month
| Month | System | Confidence |
|---|---|---|
| June | Historical (15th–20th century) | high |
Frequently asked questions
- Does "cat's eye" always mean the same gem?
- No, and this is the single most important thing to know before buying one. Used without qualification in the trade, "cat's eye" traditionally means chrysoberyl cat's eye specifically. Other species that can show the same chatoyant effect — tourmaline, quartz, apatite — are named explicitly, as "tourmaline cat's eye" and so on, precisely to avoid this ambiguity.
- What causes the "eye" effect?
- Chatoyancy comes from parallel, needle-like mineral inclusions or fine fibrous structure inside the stone. When cut as a smooth-topped cabochon, light reflecting off those parallel inclusions concentrates into a single bright line that appears to move across the stone as it's tilted, resembling a cat's slit pupil.